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 A195049 Concentric 21-gonal numbers. 7
 0, 1, 21, 43, 84, 127, 189, 253, 336, 421, 525, 631, 756, 883, 1029, 1177, 1344, 1513, 1701, 1891, 2100, 2311, 2541, 2773, 3024, 3277, 3549, 3823, 4116, 4411, 4725, 5041, 5376, 5713, 6069, 6427, 6804, 7183, 7581, 7981, 8400, 8821, 9261, 9703, 10164 (list; graph; refs; listen; history; text; internal format)
 OFFSET 0,3 LINKS Ivan Panchenko, Table of n, a(n) for n = 0..1000 Index entries for linear recurrences with constant coefficients, signature (2,0,-2,1). FORMULA a(n) = 21*n^2/4 + 17*((-1)^n-1)/8. From Colin Barker, Sep 16 2012: (Start) a(n) = 2*a(n-1) - 2*a(n-3) + a(n-4). G.f.: x*(1+19*x+x^2)/((1-x)^3*(1+x)). (End) MAPLE A195049:=n->21*n^2/4+17*((-1)^n-1)/8: seq(A195049(n), n=0..100); # Wesley Ivan Hurt, Jan 17 2017 PROG (PARI) a(n)=21*n^2/4+17*((-1)^n-1)/8 \\ Charles R Greathouse IV, Oct 07 2015 CROSSREFS Column 21 of A195040. Cf. A032527, A032528, A195048, A195148, A195149, A195058. Sequence in context: A041868 A135391 A118569 * A041874 A041872 A041876 Adjacent sequences:  A195046 A195047 A195048 * A195050 A195051 A195052 KEYWORD nonn,easy AUTHOR Omar E. Pol, Sep 27 2011 STATUS approved

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Last modified May 25 11:27 EDT 2020. Contains 334592 sequences. (Running on oeis4.)